Considering the fact that influenza was reduced by 42 percent at a dose of just 1,200 IU's a day, it's possible that even better results might be obtained with higher dosages—depending on just how deficient you are to begin with, of course, because it's not really the dosage that matters; it's the amount of vitamin D in your blood.

It's Not the Dosage that Matters—It's the Serum Level

Some 40 leading vitamin D experts from around the world currently agree that the most important factor when it comes to vitamin D is your serum level. So you really should be taking whatever dosage required to obtain a therapeutic level of vitamin D in your blood.

However, while there is no specific dosage level at which "magic" happens, based on the most recent research by GrassrootsHealth—an organization that has greatly contributed to the current knowledge on vitamin D through their D* Action Study—it appears as though most adults need about 8,000 IU'sof vitamin D a day in order to get their serum levels above 40 ng/ml. This is significantly higher than previously recommended!

For children, many experts agree they need about 35 IU's of vitamin D per pound of body weight.

At the time GrassrootsHealth performed the studies that resulted in this increased dosage recommendation, the optimal serum level was believed to be between 40 to 60 nanograms per milliliter (ng/ml). Since then, the optimal vitamin D level has been raised to 50-70 ng/ml, and when treating cancer or heart disease, as high as 70-100 ng/ml, as illustrated in the chart below.

What this means is that even if you do not regularly monitor your vitamin D levels (which you should), your risk of overdosing is going to be fairly slim, even if you take as much as 8,000 IU's a day. However, the only way to determine youroptimal dose is to get your blood tested regularly, and adjust your dosage to maintain that goldilocks' zone.

The Ideal Way to Optimize Your Vitamin D Levels

While a lot of the focus on vitamin D ends up being about vitamin D supplementation, the IDEAL way to optimize your vitamin D levels is not by taking a pill, but rather allowing your body to do what it was designed to do—create vitamin D from sun exposure.

In a recent interview, Dr. Stephanie Seneff really brought the importance of getting your vitamin D from sun exposure to the fore. While I've consistently recommended getting your vitamin D from regular sun exposure whenever possible, her input really convinced me of the wisdom of this natural strategy. She explained that when your skin is exposed to sunshine, it synthesizes not only vitamin D3, but also vitamin D3 sulfate. Your sulfur levels are intricately tied to your cholesterol levels, and plays an important role in the prevention of heart disease.

So essentially, getting regular sun exposure has much greater health ramifications than "just" raising your vitamin D levels and preventing infections. Sun exposure also appears to play a role in heart- and cardiovascular health, and much more!

The sulfated vitamin D formed in your skin in response to sun exposure is water soluble, unlike an oral vitamin D3 supplements, which is unsulfated. The water soluble form can travel freely in your blood stream, whereas the unsulfated form needs LDL (the so-called "bad" cholesterol) as a vehicle of transport. Dr. Seneff's suspicion is that the oral non-sulfated form of vitamin D may therefore not provide all of the same benefits as the sulfated form, because it cannot be converted to vitamin D sulfate...

If you cannot get your vitamin D requirements from sun exposure, I recommend using a safe tanning bed (one with electronic ballasts rather than magnetic ballasts, to avoid unnecessary exposure to EMF fields). Safe tanning beds also have less of the dangerous UVA than sunlight, while unsafe ones have more UVA than sunlight.

If neither of these are feasible options, then you should take an oral vitamin D3 supplement. It will definitely be better than no vitamin D at all.

Vitamin D Versus Flu Vaccine

Although the featured study did not make any comparison with vaccination, the 'gold standard' of scientific analysis, the so-called Cochrane Database Review, has issued no less than five reports between 2006 and 2010, all of which decimate the claim that flu vaccinations are the most effective prevention method available.

"Influenza vaccines have a modest effect in reducing influenza symptoms and working days lost. There is no evidence that they affect complications, such as pneumonia, or transmission.

WARNING: This review includes 15 out of 36 trials funded by industry (four had no funding declaration). An earlier systematic review of 274 influenza vaccine studies published up to 2007 found industry funded studies were published in more prestigious journals and cited more than other studies independently from methodological quality and size. Studies funded from public sources were significantly less likely to report conclusions favorable to the vaccines…." [Emphasis mine.]

So, despite the fact that 15 of the 36 studies included were biased by industry interests, they still couldn't come up with evidence supporting the conventional claim that flu vaccines are the best and most effective prevention available against the flu.

The Cochrane Database Review has also issued two reports each on the effectiveness of flu vaccines on infants and the elderly, and all four reviews had negative findings!

For children:

A large-scale, systematic review of 51 studies, published in the Cochrane Database of Systematic Reviews in 2006, found no evidence that the flu vaccine is any more effective than a placebo in children under two. The studies involved 260,000 children, age 6 to 23 months.

Two years, later, in 2008, another Cochrane review again concluded that "little evidence is available" that the flu vaccine is effective for children under the age of two. Even more disturbingly, the authors stated that: "It was surprising to find only one study of inactivated vaccine in children under two years, given current recommendations to vaccinate healthy children from six months old in the USA and Canada. If immunization in children is to be recommended as a public health policy, large-scale studies assessing important outcomes and directly comparing vaccine types are urgently required."

Cochrane also reviewed whether or not vaccinating health care workers can help protect the elderly patients with whom they work. In conclusion, the authors state that: "[T]here is no evidence that vaccinating health care workers prevents influenza in elderly residents in long-term care facilities.

Is Influenza a Symptom of Vitamin D Deficiency?

Getting back to vitamin D, Dr. John Cannell, founder of the Vitamin D Council, was one of the first to introduce the idea that vitamin D deficiency may actually be an underlyingcause of influenza, which would help explain its apparent benefits as a flu-fighter. His hypothesis was published in the journal Epidemiology and Infection in 2006, which was followed up with another study published in the Virology Journal in 2008.

"The findings of our study support an important role for vitamin D in prevention of common respiratory infections, such as colds and the flu. Individuals with common lung diseases, such as asthma or emphysema, may be particularly susceptible to respiratory infections from vitamin D deficiency."

The evidence supporting Dr. Cannell's hypothesis of influenza as a symptom of vitamin D deficiency is so compelling that I, for one, believe optimizing your vitamin D levels is one of the absolute best flu-prevention strategies available to date. But that's not to say it's the only factor. Your overall immune function cannot be ignored, and when it comes to maintaining optimal immune function, your diet becomes sacrosanct.

Dietary Strategies to Kick a Cold or Flu

Hopefully, you've already taken some of my dietary advice to heart and started reducing sugars/fructose and grains from your diet, which (in combination with appropriate sun exposure) will automatically help you maintain more robust immune function year-round. However, if you've been a bit lax on this point, the first thing you want to do when you feel yourself coming down with a cold or flu is to immediately cut ALL sugars/fructose, grains, artificial sweeteners, and processed foods from your diet.

Sugar is particularly damaging to your immune system -- which needs to be ramped up, not suppressed, in order to combat an emerging infection. This includes fructose from fruit juice, and all types of grains (as they break down as sugar in your body).

Ideally, you'll want to address nutrition, sleep, exercise and stress at the very first signs of 'getting a bug.' This is when immune-enhancing strategies will be most effective.